It may have seemed like a crazy idea half a decade ago, when the release of Iron Man and The Incredible Hulk within a few months of each other signalled the start of something entirely unique in the film world. Marvel Studios had begun gathering together its mightiest heroes not simply for a series of adaptations, but to reconstruct its comic book universe for cinema audiences. The so-called Marvel Cinematic Universe gained momentum with the addition of Thor and Captain America: The First Avenger to the roster, not to mention an Iron Man sequel, and suddenly the impossible seemed possible. While DC Comics struggled through Superman reboots and Green Lantern misfires, Marvel had a legitimate cinematic institution on their hands.

With The Avengers, the disparate elements from four thematically different worlds come together. When an alien force threatens the Earth, under the charge of Asgardian wild child Loki (Tom Hiddleston), über spy organisation S.H.I.E.L.D is compromised. Director Nick Fury (Samuel L. Jackson) desperately summons together Earth’s mightiest warriors to analyse the threat. Yet Captain America (Chris Evans) is a man out of time, and Tony Stark/Iron Man (Robert Downey Jr) an unstoppable egotist with other pursuits on his mind. Black Widow (Scarlet Johansson) is emotionally compromised, uncontrollable demi-god Thor (Chris Hemsworth) is conflicted when it comes to his brother Loki and the newly calm Dr. Bruce Banner (Mark Ruffalo) keeps the Hulk in check. Will this ragtag team be enough to keep the extraterrestrial hordes at bay?

Given that The Avengers is the culmination of a six film world-building saga, much of the first act of the film is confusingly spent in a dragging set-up not just for this film, but for the chapters that will inevitably follow. Indeed, one would be forgiven for thinking this was the prematurely released Iron Man 3 for at least half of the exposition. Yet as director Joss Whedon‘s script rapidly ticks off the whereabouts of all the players, getting us up to speed with their various misadventures in the cracks between films, some of the immediacy of the spectacular opening is lost. Here even master team-builder Whedon, seasoned through Buffy the Vampire Slayer and Firefly, struggles with the essential problem this film was always going to face: keeping four fan bases happy but simultaneously moving the story forward.

Once all of the pieces are in one place, however, The Avengers becomes the cracking piece of event cinema that it was always destined to be. Here Whedon plays in his element, as humour and character building mark this just as much his film as the work of Marvel Studios’ producer Kevin Feige. Downey Jr naturally gets all the best one-liners, but exchanges between him, Evans, Ruffalo and Hemsworth in particular are evenly paced and frequently side-splitting. Whedon is not afraid to use visual humour either, playing on the Hulk’s size or his ability to fling about mortals like rag dolls. More than anything, he recognises that these are already well-defined characters from previous films and comics, and allows their natural charms to emerge within the story where possible.

Hiddleston builds on his powerfully sympathetic portrayal of the conflicted villain, although the nature of The Avengers beast requires that he be a little more cut and dry in his villainy. On the flip side, Captain America’s transition back into the world after decades on ice is one that requires more exploration, but we will have to wait several years for this to eventuate in its own sequel. The only new cast member is Mark Ruffalo, who replaces Edward Norton as Bruce Banner/The Hulk. Effortlessly slipping into the role, he provides genuine warmth and a glimmer of what what has transpired to the character off-screen. Although a third standalone Hulk film is not currently on the horizon, Ruffalo is the first actor to take on the role who actually makes us want to see more of his charmingly gentle take.

Yet this is, above all things, an action film and this is where the film ultimately delivers and overwhelms. Once the invasion force descends from the heavens, the Michael Bay gene of the film takes over, favouring spectacle over all else. There is undoubtedly far more intelligence behind this action, from the Hulk’s encounters with individual enemies to Stark’s quips in the heat of battle. It would be be a cold-hearted fanboy who didn’t get all aquiver as the team comes together on the battlefield for the first time, and a giant creature snakes its way around a embattled New York. In the climactic moments, some of the cracks admittedly show. The Hulk’s domesticity is a convenient occurrence rather than a naturally occurring one, but does make for some spectacular imagery. After literally using archer Clint Barton/Hawkeye (Jeremy Renner) as a pawn in the opening chapter, Whedon is left with not having an effective place for him (or Johansson for that matter) in the final battle of super-beings.

As a cinematic achievement, The Avengers requires a firm salute of respect for giving the fans exactly what they wanted and pulling together one of the first epics of the year. Yet as fans will know, sticking around until the post-credits sequence is mandatory in a Marvels Studios film, although this time non comics readers will be left scratching their heads. Either way, what The Avengers mostly achieves is an end to one chapter and opening a door to another, filled with sequels, spin-offs and a growing legion of fans who have had their expectations raised by the unnecessarily high quality of this series.

The Avengers is released 25 April 2012 in Australia, 27 April 2012 in the UK (as The Avengers Assemble) and 4 May 2012 in the US from Disney.